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Garden Tractors Discussion Forum

decompression feature

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ed will

04-10-2018 06:28:35

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Hi, is the decompression feature on the bigger Briggs engines hooked to choke or how do they work? I have 2 - 26hp Briggs that you have to choke to get them to start. One of them has the throttle lever hooked to choke so you have to push the throttle lever all the way forward to choke and when it starts pull it back quickly or engine will be full throttle. Ed Will Oliver BC

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Brian G. NY

04-10-2018 08:12:58

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 Re: decompression feature in reply to ed will, 04-10-2018 06:28:35  
They have a centrifugally activated compression release that momentarily lifts the intake valve during starting.

If this link works, you will see how it works.


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04-10-2018 07:30:54

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 Re: decompression feature in reply to ed will, 04-10-2018 06:28:35  
Those engines likely have an extra little "nub" on the camshaft that pops the exhaust valve open a small amount for a short time just before TDC, relieving some cylinder pressure.

This is effective at cranking speed, still happens "at speed", but not enough time to have much effect, so it doesn't need to be "shut off" after starting, as Kohler did with the centrifugal ACR on the old K-series engines.

Throttle lever/choke has NO effect on the compression release function on your Briggses.

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04-10-2018 08:21:05

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 Re: decompression feature in reply to Bob, 04-10-2018 07:30:54  
Sometimes you run across an engine that will just "Lay Down" when it gets a good load on it..that suggests the valve clearance is not sufficient and the "De-Compression" is being over-done..

Just be careful adjusting the clearances..a little too much and the force needed to spin the engine over at start-up can be excessive..(but they don't lay down.!!)...

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